Conclusion 



The results of the comparative analysis of the status of the 

 plankton communities discovered in June 1981 and July 1984 

 have shown that the majority of revealed changes constituted 

 a part of the seasonal spring-summer dynamics of the structures 

 and functions of the pelagic communities in the basin under 

 consideration (Geinrikh, 1959; Kun, 1975). At the same time, 

 it is obvious that the revealed differences were determined, to 

 a certain measure, by the interannual variability of the habitats 

 of the communities. At the present stage of investigations, it is 

 not possible to distinguish between them, but we believe that 

 the seasonal variability is a determining factor; therefore, the 

 data obtained were considered in the aspect of the seasonal 

 variability. 



The structural and functional characteristics of the Bering 

 Sea plankton communities are described in detail in a monograph 

 (Izrael & Tsyban, 1990). 



Comparing the structure of the community populating the 

 deep-water southwestern Bering Sea in June 1981 and July 

 1 984, it should be noted that in the changeover from the spring 

 to summer season, the biomass of the whole community 

 decreased, on average, by a factor of 1.5, and, in particular in 

 the East Polygon, by a factor of 2 (Fig. 2). A decrease in the 

 level of the inde.x occurred primarily at the expense of phyto- 

 and bacterioplankton. Their biomass decreased by a factor of 

 2.6 and 3.0, respectively. 



The character of changes in the biomass of plankton 

 elements was not similar. Thus, at the West Polygon where the 

 epipelagic community was, due to the geographic location, at 

 an earlier stage of the seasonal development as compared with 

 other sea areas (Kulikov, 1989), the biomass of 

 microzooplankton increased by a factor of 1.7 and that of 

 mesozooplankton, by a factor of 1.2. At the same time, a 

 significant decrease of the mesozooplankton biomass (on 

 average, by a factor of 1.7) was observed at South and East 

 Polygons. As a result of the seasonal reconstruction of the 

 structure of the community, the fraction of autotrophs reduced 

 in July by a factor of 2 and that of zooplankton, vice versa, 

 increased by a factor of 1 .2 in all the investigated areas of the 

 deep-water region of the Bering Sea. 



In the shelf region of the northern Bering Sea, the trend of 

 the seasonal succession in the north sharply differed from that 

 in the south. In the south of the North Polygon, the dynamics 

 of the structure of the shelf pelagic community had the same 

 features as that in the deep-water regions (see Fig. 2). In 

 contrast, in the northern area of that polygon, in the waters of 

 the Anadyr Current, the biomass of the community increased 

 by a factor of 1 .5. This was determined by an increase in the 

 biomass of phytoplankton by a factor of 1.6 and in that of 

 mesozooplankton by a factor of 2.3. The relative values of the 

 biomass of these elements changed in the same direction, but 

 to a lesser extent. At the same time, the fraction of the biomass 

 of microheterotrophic elements decreased, on average, by a 

 factor of 3-5. 



The character of the functions of the plankton communities 

 in the surface waters of the Bering Sea also underwent a 



B,,, Kcal/m- 

 70 - 



:::-;,^OT 











IMS I 1984 

 Wesi 



l^tSl WS4 

 East 



14X1 ms4 years 



South Polygons 



phvio- 

 plankion 



baclerio- 



planklon 



microzoo- 

 plankton 



mesozoo- 

 plankton 



1981 1984 

 Northern part 



1981 1984 years, areas, polygon 

 Southern part 



Fig. 2. 



Biomass of the plankton coniiniinities (B,,) and consisting elements 

 (B)mJune 14X1 and July 1984. 



number of significant changes in July 1984 as compared to 

 June 1981. For instance, the levels ofthe overall heterotrophic 

 destruction of organic matter in the southwestern sea (South, 

 East, and West Polygons) increased by a factor of 2-5 and at 

 North Polygon by a factor of 6. So sharp an increase in the rate 

 of destruction in July was caused by a significant increase by 

 a factor of 6- 13 in the intensity of vital activity of the bacterial 

 link of the epipelagic communities. The fraction of bacterial 

 destruction in the total flu.x reached, on average, 90% in July 

 1984 versus 43% in June 1981. 



As a result of increased expenditure ofthe communities on 

 metabolism in the summer period, the balance of production- 

 destruction processes observed in spring was disturbed in the 

 epipelagic region of the deep-water sea areas and shelf water 

 masses (Fig. 3). A deficiency of newly formed organic matter 

 [P(o)] in these regions amounted to an average of 

 1 2 kcal/m- day. Attention is drawn to the fact that in spring the 

 inflow of the energy of allochthonous organic matter to the 

 community was small and did not produce a significant effect 

 on the levels of the actual production |P(act)|, and in summer 

 its volume sharply increased and covered in plenty a shortage 

 of organic matter produced in the community. Thus, for 

 instance, at the West Polygon, in the most productive waters 

 among those investigated in the deep-water sea area, the 

 average value of the actual production of the community 

 reached in June and July 1 . 1 kcal/m- day and 7.9 kcal/m- day, 



206 



